Journal of Earth Science, Vol. 32, No. 3, p. 512–523, June 2021 ISSN 1674-487X Printed in China https://doi.org/10.1007/s12583-021-1310-9

Summary of East Gondwanan Conodont Data through the Ireviken Event at Boree Creek

Andrew Simpson *1, David Mathieson2, Jiri Frýda3, Barbora Frýdová3 1. Archives and Collections, University Library, Macquarie University, Sydney NSW 2109, Australia 2. Department of Biological Sciences, Macquarie University, Sydney NSW 2109, Australia 3. Department of Environmental Geosciences, Czech University of Life Sciences Prague, 16500 Prague, Czech Republic Andrew Simpson: https://orcid.org/0000-0001-6584-6451

ABSTRACT: The Ireviken Event was the first Middle Paleozoic event consisting of synchronised faunal, isotopic and facies change to be recognised. An analysis of the conodont faunas throughout the Boree Creek/Borenore Limestone succession in the central western region of the Tasman fold belt of New South Wales (Australia) revealing all five conodont zones that comprise the event is presented. While some zonal boundaries are precise, allowing direct comparison of stratigraphic intervals on other paleo-continents, some can only be approximated. Conodont data from pre-Ireviken Event strata, in contrast, only permit the identification of a broad Telychian chronology. The identification of Wenlock post-Ireviken Event conodont zones is incomplete due to lithological variability, namely the presence of tuffaceous beds near the top of the formation and an unconformity between the Boree Creek and overlying Borenore Lime- stone. The Boree Creek Formation contains the only example of the Ireviken Event discovered to date from the Tasman fold belt of eastern Gondwanaland. KEY WORDS: conodonts, extinction, Ireviken Event, Silurian, Boree Creek, eastern Gondwanaland.

0 INTRODUCTION 2007; Munnecke et al., 2003) and the Avalonian part of Laurussia The Early Silurian Ireviken Event is one of the most pro- (e.g., Loydell and Frýda, 2007). There is one study from tropical found intervals of species turnover during the Paleozoic that Gondwana (New South Wales; Talent et al., 1993) and only two has been identified to date. Jeppsson (1990, 1984) first devel- records from higher latitudes of peri-Gondwana (Frýda et al., oped an oceanic model for the Silurian based on observed pat- 2015) and Gondwana (Vecoli et al., 2009; Wenzel, 1997). The terns of change in conodont faunas through time. He proposed only available geochemical measurements from eastern Gond- 13 two types of stable and four types of unstable oceanic states, wana are 5 elevated δ Ccarb values reported by Talent et al. (1993) the former referred to as an “episode” and the latter, an “event”. from the Boree Creek Formation, a unit of limestones and vol- He (Jeppsson, 1998) postulated strong causal links between the caniclastic sediments from the Middle Paleozoic Waugoola Group, characteristics of an event and the preceding and subsequent in the Lachlan fold belt of central western New South Wales, Aus- episodes. Events exhibited an internal architecture of datum tralia. The only closely sampled conodont data from eastern planes and step-wise sequential extinction of conodont taxa. Gondwana through this time interval also comes from the Boree Although the model was derived to explain the patterns of Creek Limestone (Molloy, 2006; Cockle, 1999; Bischoff, 1986). chronology of conodont taxa in the intensely sampled Gotland succession, geographic terms were applied to event nomencla- 1 GEOLOGICAL SETTING ture so as not to limit the effectiveness of these terms with The stratigraphy of the Boree Creek Formation has been non-specialists (Jeppsson, 1998, p. 240). considered in several papers, principally by Walker (1959), The Ireviken Event is associated with a prominent early Sherwin (1971), Talent et al. (2003a, 1993, 1975), Pickett Sheinwoodian carbonate carbon isotope anomaly that reaches up (1982), Bischoff (1986), Holloway and Lane (1998), Jell and to +5 δ13C (Munnecke et al., 2003). This perturbation of carbon Talent (1989), Cockle (1999), and Valentine et al. (2003). Tal- cycle has been reported from different parts of Laurussia, includ- ent et al. (1975) and Pickett (1982) have covered discussion on ing its Laurentian part (e.g., Brand et al., 2006; Saltzman, 2001), the relationship of the Boree Creek Formation to other units. the Baltoscandian Basin (e.g., Racki et al., 2012; Kaljo et al., The Boree Creek Formation (Sherwin, 1971) is a Silurian unit of limestones and volcaniclastic sediments forming part of *Corresponding author: [email protected] the Middle Paleozoic Waugoola Group (Pogson and Watkins, © China University of Geosciences (Wuhan) and Springer-Verlag 1998; Jenkins, 1978) in the Lachlan fold belt of central western GmbH Germany, Part of Springer Nature 2021 New South Wales, Australia. This suite of rocks is interpreted as representing a marginal platform to deep water sequence Manuscript received October 10, 2020. (Downes et al., 2013) formed through the deposition of strata Manuscript accepted May 13, 2021. from the accretion of the intra-oceanic Macquarie arc to the

Simpson, A., Mathieson, D., Frýda, J., et al., 2021. Summary of East Gondwanan Conodont Data through the Ireviken Event at Boree Creek. Journal of Earth Science, 32(3): 512–523. https://doi.org/10.1007/s12583-021-1310-9. http://en.earth-science.net Summary of East Gondwanan Conodont Data through the Ireviken Event at Boree Creek 513

Gondwana Plate (Glenn et al., 2007). thickness of up to 600 m (Pickett, 1982) that is believed to be the The Boree Creek Formation (Figs. 1 and 2) unconformably lateral equivalent of the Mirrabooka Formation and the Molong overlies volcanics and volcaniclastics of the Cheesemans Creek Limestone (Pickett, 1982; Talent et al., 1975). Formation (Sherwin, 1971) dated as Late Ordovician on grapto- Three informal units have previously been identified lite evidence (Percival and Glen, 2007; Percival et al., 2001). The within the Boree Creek Formation (Sherwin, 1971) in ascend- formation is unconformably overlain by the Borenore Limestone, ing order: (1) the lowest, limestone unit A, essentially equiva- a bedded to massive and brecciated unit of carbonates with a lent to the Rosyth Limestone of Walker (1959), consists of

Figure 1. Regional geological map of the Boree Creek area (after Cockle, 1999 and Molloy and Simpson, 2012) showing the location of Kalinga Gully and the stratigraphic sequence sampled (Fig. 3).

514 Andrew Simpson, David Mathieson, Jiri Frýda and Barbora Frýdová

Figure 2. Detailed geological map of the Kalinga Gully area studied (after Molloy and Simpson, 2012). thinly bedded nodular limestones rich in fossils including small position as Bischoff’s (1986) B Section. This work identified a brachiopods and corals topped by a reddish coarse grained major isotopic excursion corresponding to Jeppsson’s (1998, limestone (Cockle, 1999); (2) tuffaceous trilobite bed; (3) lime- 1997a, b, 1990) Datum 2 of the Ireviken Event. stone unit B, a thin to moderately thickly bedded, partially In Kalinga Gully, six separate lithological units of the Boree dolomotised interval of limestones (Bischoff, 1986). Creek Formation can be discriminated (Fig. 3). The lowermost This three-fold subdivision (Sherwin, 1971) was largely unit is a thinly bedded argillaceous limestone. The contact with adopted by subsequent authors such as Pickett (1982), Bischoff the underlying Cheesemans Creek volcanics is obscured by soil (1986), Holloway and Lane (1998) and Cockle (1999). These cover, but the unit was estimated to be approximately 40 m thick three units are easy to discriminate in the designated type sec- (Cockle, 1999), it is highly fossiliferous with pyritised fo- tion at Cheesemans Creek, however, it has been noted by a raminifers, gastropods, ostracods and brachiopods (Valentine et number of authors that lateral facies variation and interfinger- al., 2003). Algae, stromatoporoid fragments and silicified corals ing lithologies can make the identification of unit boundaries have also been reported from this interval (Valentine et al., 2003). problematic (Valentine et al., 2003; Pickett, 1982). Overlying this is a massive coarse grained red 5 m thick lime- The section studied in this investigation is the easternmost stone unit. Molloy and Simpson (2012) reported subtle differ- exposure of the Boree Creek Formation outcropping on both ences in lithology within the red limestone unit. Valentine et al. sides of Kalinga Gully, approximately 1 km from Borenore (2003) indicated that the red colour is the result of fine grained Caves (Fig. 2). This is the same section studied by Bischoff haematite iron particles and stylolites. These two units combined (1986, Section B) and also the subject of a study of lingulifor- comprise the equivalent of Sherwin’s (1971) limestone unit A mean brachiopods through the Ireviken Event (Valentine et al., (Fig. 3). Overlying the red limestone is a 5 m thick unit of 2003: BM Section). The section was resampled by Molloy fine-grained lensoidal grey limestone considered to be the basal (2006: BM Section) in a quest for better chronologic resolution portion of Sherwin’s tuffaceous trilobite bed (Fig. 3), this unit is through the event using conodonts, and for partial correlation of not present in the type section of the Boree Creek Formation. these results with intervals on other continental blocks (e.g., Valentine et al. (2003) reported that this unit is topped with a thin Molloy and Simpson, 2012). As part of an earlier investigation coarse-grained red limestone bed with abundant brachiopods and of a range of Mid Paleozoic extinction events, Talent et al. trilobites. This unit is overlain by a succession of poorly bedded (1993: BOC Section) undertook whole rock analyses for carbon tuffaceous calcareous sandstones representing the upper part of and oxygen isotopes in Kalinga Gully in essentially the same Sherwin’s (1971) tuffaceous trilobite unit. The sandstone is

Summary of East Gondwanan Conodont Data through the Ireviken Event at Boree Creek 515

Figure 3. Stratigraphic section through Boree Creek Formation and overlying Borenore Limestone showing distribution of main conodont taxa and highest resolution biostratigraphic intervals through pre-Ireviken, Ireviken and post-Ireviken strata. BM0 is located at the top of the lowermost grey limestone. The meterage of samples taken above that in the section is expressed with positive numbers, samples from within the lowermost limestone, below BM0 are ex- pressed with negative meterage measurements.

516 Andrew Simpson, David Mathieson, Jiri Frýda and Barbora Frýdová

Figure 4. Schematic diagram showing broad relationships over time between stratigraphic units in central western New South Wales discussed in the text (after Pickett, 1982). composed of sub-rounded, diagenetically altered components The late Llandovery early Wenlock interval has one of the from a reworked tuff that is set with a calcitic cement (Cockle, most profound Middle Paleozoic extinction events because of 1999). The tuffaceous beds are overlain by a 7 m interval of the impact on conodont faunas. Also known as the Ireviken dolomitic carbonates equivalent to Sherwin’s (1971) limestone Event, the stepwise faunal changes, originally identified as unit B (Figs. 2 and 3). It is more massive and sparsely fossilifer- eight datum points (Jeppsson, 1997a) in the Gotland interval, ous in comparison with underlying carbonates and, unlike other has become the basis for a new biostratigraphic scheme offer- units in the formation, appears to thicken towards the west (Val- ing higher level precision. The broad zones have been divided entine et al., 2003). These five units were identified by Valentine into new schema involving a hierarchy of biostratigraphic con- et al. (2003) who concluded that limestone unit B was uncon- cepts encompassing superzones, zones and subzones (Männik, formably overlain by the marly carbonates of the Borenore For- 2007), and also the concept of zonal groups (Jeppsson, 1997b). mation. However, in resampling to pursue additional conodont Jeppsson (1997b) identified 5 zones in a biostratigraphic data, Molloy (2006) identified another smaller tuffaceous sand- scheme based on the datum points of the Ireviken Event and stone bed overlying limestone unit B and underlying the Bore- correlated these with other successions around the world, in- nore Formation in Kalinga Gully. cluding Boree Creek. This was based on his examination of As noted above, the Borenore Formation unconformably published and unpublished faunas of Bischoff (1986). Further overlies the Boree Creek Formation in Kalinga Gully. It has a developments in our understanding of the evolution of Ptero- thickness of up to 900 m and is laterally equivalent to the primar- spathodus (Männik, 1998; Männik and Aldridge, 1989) have ily clastic Mirrabooka Formation (Pogson and Watkins, 1998). In allowed the subdivision of the Telychian pre-Ireviken interval, the area to the west of Kalinga Gully the Borenore Formation based on Baltic successions, into six zones and six subzones interfingers with the latter. The Borenore Formation consists of (Männik, 2007). two principle outcrop types. One is a well bedded, poorly out- The biostratigraphic interpretations of the Boree Creek cropping, low relief limestone, the other is a massive, high relief Section given here are primarily based on the conodont faunas and often brecciated limestone (Pickett, 1982) considered by of Molloy (2006) augmented by faunas from earlier work some to possibly be the result of debris flow emplacement (e.g., (Cockle, 1999; Bischoff, 1986) from the same interval supple- Cockle, 1999). The Borenore Formation is also considered to be mented with additional collecting by us. It is clear that the Bo- the lateral equivalent of the Molong Limestone (Adrian, 1971). ree Creek/Borenore Limestone Section in Kalinga Gully con- The Mirrabooka Formation and the Borenore Formation are both tains pre-Ireviken, Ireviken and post-Ireviken Event strata, overlain by the Wallace Shale (Fig. 4). these are discussed separately below. However, it is worth not- ing that more substantial faunas are required to accurately de- 2 BIOSTRATIGRAPHY lineate some of the high resolution biostratigraphic boundaries Silurian conodont zonation schemes were originally based within the section. on the presence of zonal index species. The late Llandovery to This analysis indicates that, although it is clear that cono- early Wenlock interval was originally based on what was inter- dont faunas and extinction patterns for the Ireviken Event are preted as the presence of two consecutive species of the genus broadly similar to the better documented and understood Pterospathodus (Walliser, 1964). While this allowed broad equivalents, particularly from Baltica, there are still some sig- global correlations, much higher level biostratigraphic preci- nificant differences, possibly paleogeographic in aspect, that sion emerged with the recognition of periods of high species require resolution before a more nuanced and advanced bio- turnover involving a stepwise succession of faunal changes stratigraphic understanding can emerge. Apart from some ap- through relatively short chronological intervals (Jeppsson, parent differences in the range of some taxa (e.g., Pseu- 1997b; Jeppsson and Männik, 1993). dooneotodus bicornis, Panderodus n. sp. N), of particular rele-

Summary of East Gondwanan Conodont Data through the Ireviken Event at Boree Creek 517 vance are the Pterospathodus faunas, specifically the absence Männik (2007: Fig. 1) reports three subspecies of Apsidog- in Australia of Pt. amorphognathoides. nathus tuberculatus that range through the Pt. eopennatus Su- Two similar species of Pterospathodus are identified in perzone and into the lower parts of the overlying Pt. celloni this study, Pt. n. sp. A and Pt. rhodesi. Männik (1998, p. 1041) Superzone. Larger populations of specimens from Boree Creek synonymised taxa from Boree Creek described by Bischoff are required for comparison with the Baltic material before any (1986) as Pt. amorphognathoides with Pt. rhodesi. While the conclusions can be drawn. respective Pa elements show some morphological similarities, Unlike the basal grey unit of the Boree Creek Formation, their stratigraphic ranges vary and the two forms co-occur in the overlying red unit has abundant conodont faunas. Bischoff one interval with Pt. n. sp. A as a distinct, but minor, constitu- (1986) documented Apsidognathus tuberculatus ssp., Aulacog- ent of the fauna. For this reason they are treated as a separate nathus borenorensis Bischoff, Distomodus staurognathoides species with the lesser known taxon kept in open nomenclature (Walliser), Pseudolonchodina borenorensis (Bishoff), Ptero- until larger faunas provide more insights on phylogeny. Se- spathodus amorphognathoides Walliser (=Pterospathodus n. sp. lected conodont taxa are illustrated in Fig. 5. A herein), Pterospathodus rhodesi Savage (=Pterospathodus latus Bischoff). Kockelella ranuliformis (Walliser) and 2.1 Pre-Ireviken Event Biostratigraphy Ozarkodina excavata excavata (Branson and Mehl) appear high In regards to the pre-Ireviken Event stratigraphy of the in the red limestone unit. Boree Creek Formation, Simpson (1995) speculated that the Molloy (2006) recorded a similar fauna from the red lime- grey limestone at the base of the Boree Creek Section (Fig. 2) stone unit (Fig. 3) including Pterospathodus pennatus procerus could be celloni Zone in age. Bischoff (1986, table 8) collated (Walliser), and the long-ranging coniform taxa Dapsilodus Pterospathodus Pa elements with platform ledges as Ptero- praecipuus Barrick, Dapsilodus obliquicostatus Branson and spathodus amorphognathoides Walliser from the grey basal Mehl, Decoriconus fragilis Branson and Mehl, Walliserodus limestone of the formation. However, both illustrated Pa ele- ssp., Panderodus recurvatus Rhodes, Panderodus unicostatus ments (Bischoff, 1986, pl. 30, fig. 19; pl. 31, fig. 22) were re- Branson and Mehl, and Panderodus langkawiensis Igo and covered from the overlying red limestone unit. Männik’s (1998) Koike. Ansella mischa Bischoff and Panderodus dueteroconus revision of Pterospathodus reconceptualised Pt. amorphogna- Bischoff were restricted to the red limestone unit as was Pseu- thoides Walliser as a succession of populations including early dobelodella silurica Armstrong, with the exception of a single forms with Pa elements lacking developed platforms (Männik, element recovered from the underlying grey limestone. Molloy 1998: p. 1015). This included a number of new zonal-specific (2006) noted Pterospathodus rhodesi Savage from the red subspecies that are recognised in European successions but not, limestone unit with a range just extending into the overlying to date, outside of Europe. limestone (i.e., Ireviken Event strata). Pterospathodus rhodesi Männik (1998) synonymised Bischoff’s (1986) examples Savage has not been recovered from the intensely sampled of Pterospathodus celloni and Pterospathodus pennatus into Baltic sections and its phylogenetic and ecological relationship the new taxon, Pterospathodus eopennatus. This species with other Pterospathodus taxa is unknown. formed the basis of the oldest Telychian Superzone. None of Based on the Pterospathodus elements from Boree Creek, these forms were reported by Bischoff (1986) from the Boree Bischoff (1986) argued that the celloni and amorphognathoides Creek Formation, either as illustrations or tabulations. Bisch- zones of Walliser (1964) should be replaced by an amended defi- off’s (1986) ‘celloni-form’ Pa elements (Bischoff, 1986, pl. 29, nition for the former (Bischoff, 1986, p. 51) and a Pterospatho- figs. 1–8) were from Quarry Creek localities and his ‘pennati- dus amorphognathoides-Pterospathodus latus Assemblage Zone form’ Pa elements (Bischoff, 1986, pl. 30, figs. 12–14, 23–30) for the latter (Bischoff, 1986, p. 54). Bischoff (1986) concluded were from Cobblers Creek localities. These are separate car- that his stratigraphically lowest 31 samples (Bischoff’s B00 to bonate units of the Waugoola Group (Pogson and Watkins, B29) and 10 samples from the overlying red limestone (his sam- 1998) cropping out to the southwest and south of the Boree ples B29 to B38) spanned the amorphognathoides-latus Zone. Creek Formation, respectively. Simpson (1995, p. 335) argued this redefinition was unnecessary Molloy (2006) recovered two Pterospathodus Pa elements because of the revision of Pterospathodus by Männik and from 12.5 and 6.8 m below the top of the basal grey limestone Aldridge (1989) that demonstrated that not all Pa elements of unit interpreted as Pterospathodus ?celloni. These elements are Pterospathodus without platform ledges were Pt. celloni. insufficient, in isolation, to allow any specific chronostrati- It is also worth noting that Molloy and Simpson (2012) graphic insights for the basal unit of the Boree Creek Formation identified a datum point (Datum Point 0) not recognised in the other than tentatively ascribing a broad Pt. celloni Superzone Gotland succession within the red limestone preceding the Ire- age. Bischoff (1986) recovered an associated conodont fauna viken Event. It was at sample BM 7.65 which marks a tempo- from the basal grey unit including Pseudolonchodina bore- rary drop in the diversity of mostly coniform conodont taxa and norensis (Bischoff), Apsidognathus tuberculatus tuberculatus the introduction of Aulacognathus chapini Savage and Walliser, Distomodus staurognathoides (Walliser), Ozarkodina Kockelella ranuliformis Walliser (Molloy and Simpson, 2012: waugoolensis Bischoff, Ozarkodina cadiaensis Bischoff and 624) with the latter recovered by Bischoff (1986) but not re- Oulodus rectangularis Bischoff. Molloy (2006) recovered a produced in the follow-up study of Molloy (2006). similar fauna but also reported the presence of long-ranging It has subsequently been shown that the evolution of coniform taxa of Panderodus and Walliserodus. Panderodus n. Kockelella is more complex than previously understood. Faunas sp. A is restricted to the basal grey limestone unit (Fig. 4). recovered to date from the Boree Creek Formation are inadequate

518 Andrew Simpson, David Mathieson, Jiri Frýda and Barbora Frýdová to determine precise ages within the Llandovery for the is only established tentatively due to the relatively few speci- pre-Ireviken strata represented by the thinly-bedded, basal, argil- mens of Apsidognathus cf. A. ruginosus found, however, the laceous grey limestone and the majority of the overlying marked decrease in abundance is down to approximately 17% coarse-grained red limestone. The latter unit obviously represents yields in comparison with the underlying sample for both coni- a late Llandovery time period due to its proximity to the Ireviken form and non-coniform taxa (Molloy and Simpson, 2012). Event and most probably represents at least in part the Ptero- Jeppsson (1998, fig. 3) equates this level with extinction of Pt. spathodus amorphognathoides amorphognathoides Zone (sensu amorphognathoides, whereas Pt. rhodesi is indicated as having Männik, 2007), whereas the basal grey limestone unit may rep- a questionably extended range slightly above this. resent strata of the Pterospathodus celloni Superzone and/or, This gives a total section interval of stratigraphic exposure towards the base of the unit, even earlier Telychian aged strata. It for the Ps. bicornis Zone at Boree Creek of around 2 m (equal to is anticipated that a higher resolution biostratigraphy will emerge 1.6 m true thickness), finer sampling would be needed to improve for the pre-Ireviken Event interval with further sampling. the accuracy of this figure. Jeppsson (1997b) correlates Bischoff’s (1986) samples B36–B38 with the Lower Ps. bicornis Zone and 2.2 Ireviken Event Biostratigraphy his samples B39, B40 with the Upper Ps. bicornis Zone. Datum 1 of the Ireviken Event is located in the red limestone The Upper Ps. bicornis Zone is followed sequentially by between BM 9.9 and BM 10.5 (Molloy and Simpson, 2012). This the Lower Pt. procerus Zone, then the Upper Pt. procerus Zone. coincides with the upper boundary of the Pt. amorphognathoides Jeppsson (1997b) noted that it is often difficult to distinguish Zone (Männik, 2007; Jeppsson, 1997b) and represents the com- between the two, this is the case with data from the Boree mencement of the Ireviken Event. The results from Molloy (2006) Creek Section. The boundary between the Upper and Lower P. show a marked decline in the abundance of conodont specimens procerus zones is Datum 4 of the Ireviken Event, this can’t be at this level. Jeppsson (1997b) identified sample B35 of Bischoff identified in the Boree Creek Formation on currently available (1986) as representing the close of the pre-Ireviken interval in data (Molloy and Simpson, 2012). The top of the Upper P. pro- Boree Creek, however the decline in the diversity of taxa is evi- cerus Zone, the equivalent of datum 6 of the Ireviken Event is dent in both samples B34 and B35. marked by the extinction of Pterospathodus and other taxa, it Datum 2, marking the upper boundary of the overlying occurs at BM 17.2 in Boree Creek. Molloy and Simpson (2012) Lower Ps. bicornis Zone, and the most dramatic reduction of recognized Datum 5 (not associated with a zonal boundary) as conodont taxa during the event, is located between BM 11.09 occurring between BM 15 and BM 15.4. We can therefore infer, and BM 11.18 (Molloy and Simpson, 2012) at the top of the red that with more extensive sampling, the boundary between the limestone (Fig. 3). This is the approximate position of the Upper Pt. procerus Zone and the Lower Pt. procerus zones in Llandovery Wenlock boundary. It coincides with the disap- the Boree Creek Formation will be located somewhere between pearance of Pterospathodus n. sp. A, Apsidognathus tubercula- BM 12.06 and BM 15. Indirect support for the interpretation of tus tuberculatus, Apsidognathus tuberculatus lobatus, Pseudo- these datum planes as boundary locations at Boree Creek is lonchodina borenorensis, Aulacognathus chapini, Oulodus given by the extinction pf Panderodus langkawienses at BM rectangularis n. ssp., and Decoriconis fragilis (which reappears 12.8. This is associated with Datum 3.3 (Jeppsson, 1998, fig. 3) higher in the section). Datum 2 is also the equivalent level of within the Lower Pt. p. procerus Zone. the upper boundary of Bischoff’s (1986) Pterospathodus The faunas of the Pt. procerus Superzone at Boree Creek amorphognathoides-Pterospathodus latus Assemblage Zone. are dominated by Pt. procerus (Walliser), various morphotypes There is a dramatic drop in conodont diversity at this level of Distomodus staurognathoides (Walliser), Kockellela ranuli- (Molloy, 2006) impacting coniform taxa including the extinc- formis (Walliser) and Oulodus rectangularis (Bischoff). This tion of Ansella mischa (Bischoff, 1997) and Panderodus deu- superzone also marks the first appearance of Ozarkodina exca- teroconus (Bischoff, 1998) and reductions in the abundance of vata excavata (Branson and Mehl). Unlike Ireviken Event fau- other Panderodus species such as P. langkawiensis Igo and nas elsewhere, Ps. bicornis does not appear in the faunas until Koike, P. n. sp. N Jeppsson and Männik and P. recurvatus BM 16.17 high in the Pt. p. procerus Zone and Panderodus n. (Rhodes). Two taxa Pterospathodus rhodesi and Apsidognathus sp. N does not become extinct at Datum 3, the close of the Ps. cf. A. ruginosus are found in very small numbers in strata di- bicornis Superzone, but persists to the lower parts of the Upper rectly above Datum 2. While this datum is known elsewhere for Pt. p. procerus Zone, i.e., up to Datum 5, as a very minor con- the extinction of Apsidognathus taxa, this Apsidognathus taxon stituent of the fauna. Jeppsson (1997b) noted the presence of is aberrant. Datum 2 representing the upper boundary of the the Lower Pt. p. procerus Zone in Bischoff’s (1986) samples Lower Ps. bicornis Zone is best interpreted, in the absence of B41 and B42 and the Upper Pt. procerus Zone in sample B45. the nominate species, as at this level, with the largest extinction Before the recognition of the internal architecture of the Ire- impact. viken Event and its utility in high resolution biostratigraphy, Datum 3 represents the upper boundary of the Upper Ps. Bischoff (1986) recognised the K. ranuliformis Zone as the oldest bicornis Zone, and the Ps. bicornis Superzone, the oldest Wenlock Zone in the Boree Creek Section. He (Bischoff, 1986, p. Wenlock conodont superzone, it is located between BM 12.00 58) adapted and modified the definition of Barrick and Klapper and BM 12.06 in the light grey limestone (Molloy and Simpson, (1976) by redefining the base of the zone with the closure of the 2012). This is tentatively established between 12.00 and 12.06 previous zone. The lower part of this zone is now recognised as where there is a decrease in abundance of most species and the part of the final (youngest) strata of the Ireviken Event. last occurrence of Apsidognathus cf. A. ruginosus. This datum

Summary of East Gondwanan Conodont Data through the Ireviken Event at Boree Creek 519

2.3 Post-Ireviken Event Biostratigraphy limestone (Cockle, 1999, BOR1 Section). Cockle (1999) re- The upper boundary of the Ireviken Event is marked by ported the occurrence of K. ranuliformis and K. variabilis Datum 8 and equates with the upper boundary of the Lower K. fragments from the stratigraphically highest occurrence of the ranuliformis Zone. Molloy and Simpson (2012) argued that on Borenore Formation investigated (BN28 Section). Simpson available data this boundary can’t be identified with any certainty (1995) had previously indicated the presence of a morphotype in the Boree Creek Section and speculated that the boundary of K. ranuliformis in the mid Ludlow of Australia that largely representing the closure of the event might have occurred during retains the same morphology, so the co-occurrence with K. the deposition of the tuffaceous sandstone unit. Above this level variabilis is possible. the post-Ireviken faunas of both Bischoff (1986) and Molloy Elsewhere in the Borenore Formation equivalent, the Mir- (2006) are sparse, it is difficult to identify the zonal scheme of rabooka Formation, Cockle (1999, BUN Section) reported the Jeppsson (1997b). However, Jeppsson (1997b) suggested that the occurrence of two faunas, an amorphognathoides Zone fauna uppermost carbonates in the Boree Creek Formation have faunas and a younger fauna with long-ranging Silurian conodont taxa. equivalent to the Upper K. ranuliformis Zone noting that the The Mirrabooka shales enclosing this carbonate ‘pod’ have Lower K. ranuliformis Zone can be seen in Bischoff’s (1986) yielded mid-Ludlow, scanicus to leintwardinensis Zone, grap- B46 sample and the Upper K. ranuliformis Zone is probably tolites (Sherwin, 1971). The carbonates from the BUN Section represented in samples B63 to B77. (Cockle, 1999) can therefore be interpreted as cannibalised Bischoff (1986) identified two distinct sequential faunas in equivalents of the Boree Creek Formation (Fig. 1). his K. ranuliformis Zone, but did not separate them into formal The conodonts, from the top of the Borenore Formation subzones. The main difference between the two faunas is the (Cockle, 1999, BN28 Section) include Kockelella variabilis giv- single taxon of Kockelella (i.e., K. ranuliformis) in the lower- ing a maximum Ludlow age for the unit. Graptolites from the most parts of the range, and multiple taxa of this genus in the Wallace Shale, conformably overlying the Mirrabooka Formation higher parts of the zone. Evolutionary developments in the east of ‘Mirrabooka’ homestead, were considered to be of late genus Kockelella were the basis for subdividing much of the Přídolí age by Sherwin and Rickards (2002) specifically repre- Wenlock and early Ludlow of North America (Barrick and senting the Monograptus perneri/M. transgrediens biozones in Klapper, 1976). For most of the Boree Creek Formation above the lower half of the formation. Pogson and Watkins (1998, p. the Ireviken Event, only the single taxon of Kockelella has been 131) stated that the upper part of the Wallace Shale probably recovered. However Bischoff (1986, table 9) recovered a single extends into the Early Devonian. Cockle (1999) reported a spot element of Kockelella latidentata Bischoff from the uppermost sample from a carbonate within the Wallace Shale, some 100 m sample of the formation and a small number of Kockelella n. sp. above the base of the unit, where it conformably overlies the A, near the top of the unit. Molloy (2006) however, only re- Mirrabooka Formation. This sample yielded Belodella anomalis covered K. latidentata Bischoff from the basal sample of the Cooper, Belodella coarctata and Coryssognathus dubius. This overlying Borenore Formation, but did record the presence of K. fauna can be interpreted as either late Ludlow or Přídolí. It is the walliseri (Helfrich) from limestone unit B in the upper reaches youngest Silurian conodont fauna recovered from the region to of the Boree Creek Formation. Much larger faunas are required date. But, like the underlying Mirrabooka Formation, the Wallace to test the more recent evolutionary scheme for this genus Shale also contains carbonates that are clearly allochthonous (Serpagli and Corradini, 1999) for this taxa to be biostrati- blocks derived from pre-existing carbonate platform successions graphically useful in the Boree Creek Section. (Fig. 1). Talent and Mawson (1999, TEZ Section) documented an Immediately above the unconformity, the limestones of the Early Silurian conodont fauna similar to the Boree Creek Forma- Borenore Formation have faunal elements from the uppermost tion with Distomodus staurognathoides, K. ranuliformis, Pan- K. patula Zone (Jeppsson, 1997b) and higher still, faunal ele- derodus greenlandensis, Panderodus n. sp. A and Ozarkodina ments similar to the uppermost K. walliseri range are present excavata excavata. Talent and Mawson (1999, Text Fig. 2) ar- (Jeppsson, 1997b). Bischoff (1986, p. 61) indicated the pres- gued that the Barnby Hills Shale is a junior synonym for the ence of the Sheinwoodian K. amsdeni Zone within the Bore- Wallace Shale and this carbonate block (TEZ Section) was de- nore Formation (samples B121–B129). Higher still (samples rived from the Nandillyan Limestone. The Wallace Shale can be B152 and B164), Bischoff (1986, p. 62) records elements of the considered as representing the terminal flooding facies of a Silu- Ludlow taxon Kokelella variabilis Walliser. Jeppsson (1997b, p. rian transgression over much of the northern Molong Rise 103) however noted this identification could be problematic. (Pickett, 1982). Jeppsson (1997b) concluded that the highest of Bischoff’s (1986) samples (sample 175) may be close to the boundary of 3 CONCLUDING REMARKS the Homerian O. s. sagitta Zone. As is seen in many other parts of the world, the sequential Away from the Kalinga Gully Section Cockle (1999) also conodont extinctions through the Ireviken Event in the Boree studied the Borenore Limestone and retrieved some conodont Creek Limestone are marked by high δ13C values particularly data. The DSC Section (Cockle, 1999, p. 115–116) was consid- from the Upper Ps. bicornis Zone through to the end of the Ire- ered to extend throughout the entire Borenore Formation, yields viken Event (Frýda et al., 2019; Frýda et al., in preparation). The were poor but both Kokelella ranuliformis and K. amsdeni were linked and synchronous changes in geochemistry, biostratigraphy reported. Kockelella ranuliformis was also reported from a and facies have been well documented for the Ireviken Event in short section within the Borenore Formation that crossed from many parts of the world. Geochemical data has been known from the well-bedded low relief limestone to the massive brecciated Baltica (e.g., Munnecke et al., 2003; Loydell, 1998; Kaljo et al.,

520 Andrew Simpson, David Mathieson, Jiri Frýda and Barbora Frýdová

Figure 5. Boree Creek Plate explanation. A. Apsidognathus tuberculatus (Walliser, 1964), upper view of Pa element, AMF131096 from BM 9.9; B. Apsidognathus tubercu- latus lobatus Bischoff, 1986, upper view of Pa element with extended anterior lobe, AMF131108 from BM 9.9; C. Aulacognathus chapini Savage, 1985, upper view of (?gerontic) Pa element, AMF131153 from BM 11.9; D. Distomodus staurognathoides (Walliser, 1964), upper view of Pa element (gamma morphotype), AMF131182 from BM 12.06; E. Kockelella ranuliformis (Walliser, 1964), upper view of Pa element, AMF131202 from BM 12.5; F. Kockelella walliseri (Helfrich, 1975), upper view of Pa element, AMF131212 from BM 60; G. Ozarkodina cadiaensis Bischoff, 1986, oblique lateral view of Pa element, AMF131218 from BM 5.05; H. Ozarkodina waugoolaensis Bischoff, 1986, inner lateral view of Pa element, AMF131246 from BM 21.4; I. Ozarkodina excavata excavata (Branson and Mehl, 1933), lateral view of Pa element, AMF131214 from BM 60.3; J. Pseudooneotodus tricornis Drygant, 1974, upper view of dextral element, AMF131251 from BM 11.09; K. Pseudooneotodus panuarensis Bischoff, 1986, upper view, AMF131257 from BM 12.5; L. Pseudooneotodus bicornis Drygant, 1974, upper view of dextral element, AMF131252 from BM 16.8; M. Ptero- spathodus n. sp. A, upper view of Pa element, AMF131261 from BM 4.4; N. Pterospathodus pennatus procerus (Walliser, 1964), upper view of Pa element, AMF131271 from BM 12.5; O. Pterospathodus rhodesi Savage, 1985, upper view of Pa element, AMF131316 from BM 3.65; P. Pterospathodus rhodesi Savage, 1985, upper view of Pa element, AMF131265 from BM 6.1; Q. Ansella mischa Bischoff, 1997, outer lateral view of geniculate element, AMF130973 from BM 10.9; R. Panderodus greenlandensis Armstrong, 1990, inner lateral view of aq element, AMF131020 from BM 63.5; S. Panderodus langkawiensis (Igo and Koike, 1967), lateral view of Sa element, AMF131027 from BM 11.09; T. Pseudooneontodus boreensis Bischoff, 1986, posterior view of slender element, AMF131259 from BM 11.09; U. Pseudobelodella silurica Armstrong, 1990, outer lateral view of ap element, AMF131054 from BM 3.65; all scale bars=100 μm.

Summary of East Gondwanan Conodont Data through the Ireviken Event at Boree Creek 521

1997; Wenzel and Joachimski, 1996), Avalonia (e.g., Loydell and 179–198 Frýda, 2007), Laurentia (e.g., Cramer and Saltzman, 2005) but Armstrong, H. A., 1990. Conodonts from the Upper Ordovician–Lower the only geochemical results to date for east Gondwanaland are Silurian Carbonate Platform of North Greenland. Bulletin, Grønlands those documented by Talent et al. (1993). The Boree Creek For- Geologiske Undersøgelse, 159: 1–151 mation is the most prospective section discovered to date in the Barrick, J. E., Klapper, G., 1976. Multielement Silurian (Late Llandoverian- Tasman fold belt for understanding changes in conodont faunas Wenlockian) Conodonts of the Clarita Formation, Arbuckle Mountains, during the Ireviken interval. Oklahoma, and Phylogeny of Kockelella. Geologica et Palaeon- In other areas of the Tasman fold belt of eastern Australia, tologica, 10: 59–100 autochthonous successions of carbonates of an appropriate age Bischoff, G. C. O., 1997. Amelia mischa n. sp. (Conodonta) from Late are poorly known. In the northern parts of the fold belt, late Llandoverian and Early Wenlockian Strata of Midwestern New South Llandovery to early Wenlock conodonts are documented mostly Wales. Neues Jahrbuch für Geologie und Paläontologie-Monatshefte, from allochthonous sources (Talent et al., 2003b; Simpson, 1997(8): 477–488. https://doi.org/10.1127/njgpm/1997/1997/477 1999; Sloan et al., 1995) although one poorly constrained suc- Bischoff, G. C. O., 1998. New Species of Panderodus (Conodonta) from Late cession at the base of the Jack Group in the Broken River Llandoverian and Early Wenlockian Strata of Midwestern New South Province is known (Talent et al., 2002). In the southern region Wales. Neues Jahrbuch für Geologie und Paläontologie-Abhandlungen, of the fold belt, Simpson and Talent (1995) speculated that the 210(2): 267–288. https://doi.org/10.1127/njgpa/210/1998/267 McCarty Member of the Towanga Formation could transgress Bischoff, G. C. O., 1986. Early and Middle Silurian Conodonts from Mid- the Llandovery-Wenlock boundary and provided evidence that western New South Wales. Courier Forschungsinstitut Senckenberg, the lower carbonate unit of the Claire Creek Limestone could 89: 1–337 extend into “post-amorphognathoides” Zone strata. Vandenberg Brand, U., Azmy, K., Veizer, J., 2006. Evaluation of the Salinic I Tectonic, (1998) suggested that all the carbonates in this area could be Cancañiri Glacial and Ireviken Biotic Events: Biochemostratigraphy of allochthonous, but Talent et al. (2003a) and Simpson and Talent the Lower Silurian Succession in the Niagara Gorge Area, Canada and (1996) argued the succession is stratigraphically and chrono- USA. Palaeogeography, Palaeoclimatology, Palaeoecology, 241(2): logically coherent. 192–213. https://doi.org/10.1016/j.palaeo.2006.03.004 The relationship between these Silurian extinction events, Branson, E. B., Mehl, M. G., 1933. Conodont Studies No. 1: Conodonts such as the Ireviken at Boree Creek, with glaciations, sea-level from the Bainbridge (Silurian) of Missouri. University of Missouri change, oceanic turnover and euxinia remains unclear in terms of Studies, 8(1): 39–52 causality. Trotter et al. (2016) provided a discussion about the Cockle, P., 1999. Conodont Data in Relation to Time Space and Environ- limitations of different data sets but concluded that global climate mental Relationships in the Siluran (Late Llandovery-Ludlow) Succes- change played an important role in producing these phenomena. sion at Boree Creek (New South Wales, Australia). Abhandlungen der Geologischen Bundesanstalt, 54: 107–133 ACKNOWLEDGMENTS Cramer, B. D., Saltzman, M. R., 2005. Sequestration of 12C in the Deep We are grateful for the excellent figures produced for this Ocean during the Early Wenlock (Silurian) Positive Carbon Isotope article with flair by Dean Oliver. We thank Leone Knight, the Excursion. Palaeogeography, Palaeoclimatology, Palaeoecology, owner of the Kalinga property near Orange for allowing access 219(3/4): 333–349. https://doi.org/10.1016/j.palaeo.2005.01.009 to the site to collect geochemical and conodont samples during Downes, P. M., Colquhoun, G. P., Blevin, P. L., et al., 2013. Bathurst 1 : field work in 2018. We thank Joanne Simpson for organising 250 000 Metallogenic Map (2nd Edition), Geological Survey of New logistics for this collecting. New sampling in 2018 was sup- South Wales, Sydney ported by the Grant Agency of Czech Republic (No. Drygant, D. M., 1974. Simple Conodonts from the Silurian and Lowermost GA17-18120S). This work builds on long term paleontological Devonian of the Volyno-Podolia. Paleontologicheskii Sbornik, 10(2): interest in the area by MUCEP (Macquarie University Centre 64–70 for Ecostratigraphy and Palaeobiology), a former research cen- Frýda, J., Lehnert, O., Joachimski, M., 2015. First Record of the Early tre at Macquarie University that undertook extensive Middle Sheinwoodian Carbon Isotope Excursion (ESCIE) from the Barrandian Paleozoic research activity under the leadership of Emeritus Area of Northwestern Peri-Gondwana. Estonian Journal of Earth Sci- Professor John Talent and the late Ruth Mawson. In particular, ences, 64(1): 42–46. https://doi.org/10.3176/earth.2015.08 this article builds on the work of our good friend and close Frýda, J., Simpson, A. J., Frýdová, B., 2019. First Complete Record of the colleague, the late Peter Molloy, who undertook his PhD stud- Early Sheinwoodian Carbon Isotope Anomaly from Australia. In: Petti, ies on conodont faunas recovered from Kalinga Gully. We F. M., Innamorati, G., Carmina, B., eds., 3rd International Congress on dedicate this paper to his memory. Specimens illustrated form Stratigraphy-Strati 2019: Abstract Book. Societa Geologica Italiana, part of a larger study on the conodonts of the Boree Creek Milan Formation, they will be lodged in the collections of the Austra- Glen, R. A., Meffre, S., Scott, R. J., 2007. Benambran Orogeny in the East- lian Museum, Sydney and are identified by their AMF numbers. ern Lachlan Orogen, Australia. Australian Journal of Earth Sciences, The final publication is available at Springer via 54(2/3): 385–415. https://doi.org/10.1080/08120090601147019 https://doi.org/10.1007/s12583-021-1310-9. Helfrich, C. T., 1975. Silurian Conodonts from the Wills Mountain Anticline, Virginia, West Virginia, and Maryland. Geological Society of America, REFERENCES CITED Special Paper, 161: 1–82 Adrian, J., 1971. Stratigraphic Units of the Molong District, New South Holloway, D. J., Lane, P. D., 1998. Effaced Styginid Trilobites from the Wales. Geological Survey of New South Wales, Records, 13(4): Silurian of New South Wales. Palaeontology, 41(5): 853–896

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